Return apparatus for a two-stage refrigeration system



July 8, 1958 wf v. RICHARDS 2,841,952

RETURN APPARATUS F OR A TWO-STAGE REFRIGERTION SYSTEM Filed Jan. 2s,1957 0N. RM, @QN NNN @l l im@ EN; Euhm,

bw NS| ,Kul

United States atent O M RETURN APPARATUS FR A T WO-STAGE REFRGERATENSYSTEM William V.. Richards, Glenview, Ill., assigner to H. A. Phiiiips,doing business as H. A. Phillips d; Company, Chicago, lll., by WaylandPhillips, conservator of his estate Application January 23, 1957, SerialNo. 635,859

9 Claims. (Cl. 62-1'74) The invention relates to refrigeration systemsof the large capacity type designed for commercial installation and hasreference more particularly to an improved liquid 1 return apparatus fora two-stage refrigeration system.

The type of refrigeration system to which the improved liquid returnapparatus may be applied is characterized by high and low temperatureevaporators, by a high stage compressor and by a pair of boostercompressors. One booster compressor is employed for increasing thepressure of the gaseous refrigerant received from the accumulator andwhich is eventually delivered to the high stage compressor. The otherbooster compressor has connection with a liquid refrigerant dump trapfor withdrawing the gaseous refrigerant from the trap and for deliveringsaid refrigerant under pressure to an ejector, the said ejector havingoperation for pumping the liquid refrigerant received from theaccumulator to the dump trap. One of the problems presented in theoperation of a refrigeration system as described has been the protectionafforded the compressor in preventing the delivery through the suctionline of liquid refrigerant to the compressor either as slugs of liquidor as smaller particles of liquid entrained with the gaseousrefrigerant. Accordingly an object of the invention is to provideimproved liquid return apparatus for a two-stage refrigeration system ofthe type having a high temperature evaporator and a low temperatureevaporator and wherein the apparatus will permit the continuousoperation of the evaporators in a flooded condition with adequate safetyto the compressor and with increased operating elhciency, all in anautomatic manner, so as not to require the constant supervision of anattendant.

Antoher object of the invention is to provide liquid refrigerant returnapparatus designed especially for a twostage system and which willemploy an accumulator in the suction line and a dump trap in therefrigerant line for handling the liquid refrigerant in a manner tocollect the same in the suction line and deliver the liquid to thereceiver or at some other location in the high pressure refrigerantline.

A further object is to provide apparatus as described wherein thebooster compressor having connection with the dump trap is employed inconjunction with an ejector which will utilize the kinetic energy in thehigh pressure gaseous refrigerant from the compressor to pump liquidrefrigerant received from the accumulator and for delivering the same tothe trap, thus obviating the need for mechanical liquid pumps which aresometimes objectionable due to maintenance problems. However, theejector requires little if any attention and is highly satisfactory inhandling oil and two phase liquids.

Another object resides in the provision of liquid refrigerant returnapparatus in combination with defrosting mechanism for one or both ofthe evaporators and which mechanism will make use of the dump trap as adepository for the liquid refrigerant forced from the evaporator coilsduring the defrosting operation. 'Ihis provides savings in 2,841,962Patented July 8, 1 958 ICC the return of useful liquid to the feed linesfor use in the i plant evaporators.

to permit discharge of the liquid refrigerant during theA defrostingoperation but which will automatically hold back the flow of the gaseousrefrigerant atan intermediate pressure.

A further object is to provide a suction line liquid refrigerant returnapparatus wherein improved means are provided for collecting andconveniently removing oil from the several evaporators comprising therefrigerating system.

With these and various other objects in view, the invention may consistof certain novel features of construction and operation, as will be morefully described and particularly pointed out in the specification,drawings and claims appended hereto.

In the drawings, which illustrate an embodiment of the device andwherein like reference characters are used to designate like parts-Figure 1 is a diagrammatic View of a refrigerating system of thetwo-stage type and which embodies the improved features of the presentinvention; and

Figure 2 is a view, parts being shown in section, of an ejector such asemployed in connection with the present accumulator.

Although the improvements of the invention may be applied torefrigeration systems of various types, the system of Figure l has beenselected for illustration. The high stage compressor designated bynumeral 10 receives gaseous refrigerant at a relatively low pressurefrom the return conduit 11, and as a result of the pumping action of thecompressor, the said gaseous refrigerant is delivered to conduit 12 at aconsiderably higher pressure and likewise its temperature iscorrespondingly increased. The high-temperature, high-pressure gaseousrefrigerant is delivered by the feed line 12 to an oil separator 14having the oil discharge pipe 15 provided with the hand valve 16 andfrom which the separated oil may be periodically drained. The feed line12 has connection at 17 with the condenser 18 and the condenser in turnis joined by conduit 20 with the liquid refrigerant receiver 21. Beyondthe condenser the feed line 12 connects with the two-Way valve 22. Saidvalve is solenoid actuated and in one position thereof the valveconnects the feed line 12 with conduit 23 leading to the dump trap 24and in its second position the valve connects the dump trap throughconduit with the low pressure suction line 25. The dump trap is equippedwith the oat switch 26 of any suitable construction and the actuation ofthis switch controls the solenoid valve 22. The liquid refrigerantcollecting in the dump trap is delivered to receiver 21 through conduit27, which in turn is equipped With the check valve 28, permitting flowin one direction only, that is, from the dump trap to the receiver. Thepipe 30, having the hand valve 31, depends from the bottom of the dumptrap and the same may be periodically opened for draining oil from thetrap.

The liquid refrigerant from the receiver is conducted by conduit 32 toan intercooler tank 34. The float valve 35 for said tank has connectionwith conduit 32 at 36 and accordingly the tank contains liquidrefrigerant at a level as determined by the float valve 35. Beyond thefloat valve connection the conduit 32 enters the intercooler tank and acoil is formed therefrom identified by numeral 37 and which is disposedadjacent the bottom of the tank so as to be submerged 'at all times inthe liquid refrigerant within the tank. The pipe 38, having the handvalve 39, is provided for draining oil from the intercooler tank. Beyondthe intercooler 34 the liquid refrigerant feed line 32 provides a headerfor parallel connection with a pair of evaporators identified bynumerals 40 and 43, the former designating the high temn peratureevaporators. Conduit 45 leads from the liquid refrigerant feed line 32and has connection in turn with the surge drum 47 for the evaporatorfill. Said evaporator includes cooling coils 41 and 42 having the supplyconduits 48, 49, and which connect with the conduit 5d, depending fromthe bottom of the surge drum. Conduit 50 is provided with the hand valve51 so as to drain oil from the drum. The cooling coils of the evaporator40 are additionally provided with a return conduit 52 land 53,respectively, and the surge drum i7 at its top has connection throughpipe 54 with the suction line return conduit 56. Said return conduitenters the intercooler tank 34 and terminates below the level of theliquid refrigerant therein so that the gas and any particles of liquidrefrigerant which may be returning with the gas lare discharged into theliquid refrigerant within the cooling tank. The gas bubbles up throughsaid liquid and is eventually returned to the high stage compressor tthrough the return conduit 11. Conduit also has connection with conduit56 at a point beyond the hand valve 55 and said conduit 57 connects withthe low pressure suction line 2S. A hand valve 53 is located in conduit57 and there is also located in this conduit a onc-way check valve S9,the same permitting flow of gaseous refrigerant in one direction only,that is, in a direction to discharge into the intermediate pressuresuction line 25 during venting of the dump trap 24.

Conduit 60, in parallel with conduit 46, supplies liquid refrigerant toevaporator 43, the same conduit connecting with the surge drum 61 fromwhich the liquid refrigerant is delivered to the cooling coils 44 andd5. The vertical conduit 62 depends from the surge drum and the supplypipes 64 and 65 connect therewith and lead to the cooling coils. Eachsupply pipe has a check valve such as 66 and 67, respectively,interposed therein so that the liquid will flow in one direction only,that is, toward the cooling coils. For defrosting the cooling coils adischarge conduit is provided, designated by numeral 63, and which isconnected toeach supply conduit through a check valve such as 70 :and71, the discharge conduit 68 in turn leading to and connecting with thesupply line 72 for the dump trap. More particularly, the check valves 70and 71 normally close during flow for refrigeration purposes althoughthey have a special construction and which may best be described asspring loaded in a manner so as to permit discharge of the liquidrefrigerant during the defrosting operation, holding back at anintermediate pressure, however, to prevent excess flow of the gaseousrefrigerant past the valve. The said check valves 70 and 71 may be setfor a pressure of approximately sixty pounds per square inch orsomewhere within this range and it will therefore be seen that fornormal operation the liquid will flow through the check valves 66 and 67to enter and flood the evaporators with the evaporated gas escapingthrough the return conduits 75 and 76 and being eventually returned tothe surge drum 61. Both surge drums (i7 and 6l function on the order ofa gas-liquid separator and said drums each include a float valve forcontrolling the supply of liquid refrigerant thereto and its levelwithin the drum which is generally set at a limit to maintain thecooling coils in a flooded condition.

When operating in a manner as described the pressures on the liquidrefrigerant in the supply pipes 64 and 65 are not sufficient to causethe check valves 70 and 71 to open. However, for defrosting the coolingcoils the high pressure gaseous refrigerant at approximately one hundredand eighty-five pounds per square inch pressure for ammonia is admittedfrom the feed line 12 to the conduit 73 by opening hand valve 79 and byopening either of the hand valves 3ft and 8l. Generally one cooling coilis permitted to operate while the other is being defrcsted, although asregards the mechanism of the present system, both coils cc-uld bedefrosted at the same time. From hand valve 30 the conduit S2 connectswith the twoway valve 33 and in a similar manner valve S1 is connectedwith a two-way valve 34 through conduit 5. When the cooling coils arebeing refrigerated the two-way valves connect the return lines 75 and 76with the surge drum 61. For a defrosting operation the two-way valvesare actuated to connect the return lines 75 and 76 with the conduits 32or 85 and thus hot gaseous refrigerant at a high pressure can besupplied to the cooling coils for defrosting them. lt will be observedthat the gaseous refrigerant is supplied in a direction opposite to thenormal ow of the liquid refrigerant through the cooling coils and thusthe check valves 66 land 67 prevent dow back to the surge drum. Sincethe pressures on the liquid refrigerant in the cooling coils will exceedthe limit for which the special check valves 70 and 71 may have beenset, the said check valves will open to allow the liquid refrigerant toflow to the dump trap. However, when the gaseous refrigerant in thecooling coils reaches the special check valves they close, thus trappingthe hot gaseous refrigerant in the cooling coils for defrostingpurposes. The defrosting operation for any coil may last approximatelytwenty to thirty minutes and the two-way valves S3 and 84 may becontrolled by a time clock having operation to energize the valvesalternately but only once during each twenty-four hour period.

ln accordance with the present invention the surge drum 61 at its topend is provided with the low pressure return conduit Se, having the handvalve 39, and which connects with the accumulator supported by thestandpipe 9i and having the level responsive float switches 92 and 93associated therewith. The gas and liquid refrigerant discharged from theend of conduit 88 is directed against .a plate 9d to help evaporate theliquid. However, some liquid refrigerant will accumulate and fllstandpipe 91 to which the conduit 95 is connected and this liquid will'ne delivered to the ejector @6, consisting of housing 97 and theinternal nozzle 98. Gaseous refrigerant is supplied to nozzle 98 by thedump trap compressor 100, the gas flowing through refrigerant line 101,and which is shaped to provide a loop, thus preventing .any liquidrefrigerant from the ejector from flowing in a reverse direction andreaching the compressor 100. The operation of the ejector is such as topump the liquid refrigerant received from the accumulator through thesupply line 72 and said liquid together with the gas is delivered to thedump trap 24. From the trap the liquid refrigerant is periodicallydelivered to the receiver, whereas, the gaseous refrigerant is Withdrawnthro-ugh line 25 by the compressor lo@ and following compression the gasis `again fed to the ejector for another pumping operation.

The gaseous refrigerant collects in the top of accumulator 90 and thisgas is drawn off through conduit 102, having the hand valve 103interposed in said line. Conduit 102 has connection with the boostercompressor 104 and said gaseous refrigerant in passing through thecompressor has its pressure increased and is eventually delivered toconduit llS provided with the hand valve 106. The said conduit 105connects with an oil separato- 107 which may be water cooled orrefrigerated in some other manner. From the oil separator 07 the conduit105 connects with the return conduit 56.

It may be desirable in the event of slop over in the high temperatureevaporator to drain the liquid refrigerant from the intercooler tank 34and return this liquid refrigerant to the system where it can expend itsenergy in cooling the evaporators. For this purpose the conduit .11,0 isprovided, the same connecting at its left hand end with the intercooler.tank and having connection at its right hand end with the conduit 88leading to accumulator 90. The interccoler tank is provided with thelevel responsive float valve 111 which in turn has connection with valve112. When the liquid level within the intercooler tank 34 reaches theelevation of float valve 111 it causes the valve to open, admitting theliquid refrigerant to valve 112. Said valve 112 is spring urged in aclosing direction and is thus normally closed. However, the effect ofthe liquid refrigerant from valve 111 and the difference in pressurebetween the inter- .cooler and the accumulator will cause 112 to openand the liquid refrigerant above the level of float 111 will thereforebe supplied to the accumulator. A check valve 114 is located to theright of valve 112 and to the left of the same there is provided a handvalve 115.

In operation of the refrigeration system as above described it will beappreciated that the dump trap in combination with the accumulator havea unique mode of operation for removing liquid refrigerant from theevaporated refrigerant returning in the suction line and which willemploy the high pressure gaseous refrigerant from the feed line forperiodically delivering the separated liquid refrigerant to thereceiver. It has been previously explained that the dump trap willreceive liquid refrigerant from the conduit 72 and during this operationthe solenoid valve 22 will have a position to allow the gaseousrefrigerant to return to the compressor 10i) through the suction line25. When liquid refrigerant within the dump trap reaches a predeterminedlevel the float switch 26 will be actuated to in turn energize valve 22and with hand valve 19 being open high pressure gaseous refrigerant fromthe feed line will be admitted to the dump trap to thereby force theliquid refrigerant through conduit 27 into receiver 21.

The dump trap is employed in combination with an accumulator which mayhave connection with one or with both of the surge drums such as 47 and61. For purposes of illustration accumulator 90 is shown connected tosurge drum 61 for the low temperature evaporator. The velocity of thegaseous refrigerant in this evaporator is particularly high and the saidgaseous refrigerant thereby entrains a considerable quantity of liquidrefrigerant in the form of small particles or droplets. These would b-einjurious if they were returned directly to the compressor andaccordingly the function of the accumulator is to effect separationbetween the gas and the liquid with the liquid refrigerant beingeventually reutrned by the ejector to the dump trap and the gaseousrefrigerant being withdrawn from the accumulator by the boostercompressor 104.

Although some liquid refrigerant will escape with the gas from the surgedrum 47 the same can be taken care of in a convenient and practicalmanner by interposing an intercooler in the suction line 56. Theintercooler performs a dual function, namely, that of cooling therefrigerant in feed line 32, for which purpose the coil 37 is provided,and also that of separating the liquid refrigerant from the gas beingdelivered thereto through the returning suction line 56.

Operation of the compressor 100 will be intermittent since it iscontrolled by the float switch 92 on the accumulator 90. When the liquidrefrigerant within the accumulator reaches a preset upper limit the oatswitch will start operation of the compressor and the same will continueuntil the liquid level drops to a point causing the float switch 92 toopen the circuit to the compressor motor. ln the event liquidrefrigerant should accumulate in 9d beyond the preset upper limit,notwithstanding the pumping action of the ejector 96, the limit switch93 is provided as a safety since closing of this switch will sound analarm, thereby notifying the operator of this condition.

The invention is notto be limited to or by details of construction ofthe particular embodiment thereof illustrated by the drawings, asvarious other forms of the device will of course be apparent to thoseskilled in the art without departing from the spirit of the invention orthe scope of the claims.

What is claimed is:

l. ln a refrigerating system, the combination with a high stagecompressor, cooling coils providing a high temperature evaporator andother separate and independent cooling coils providing a low temperatureevaporator, of a surge drum for each of said cooling coils havingoperation to maintain its respective cooling coils in a floodedcondition for refrigerating purposes, a high pressure refrigerant feedline from said compressor and providing parallel connections to thesurge drums, a suction line for each surge drum for returning evaporatedrefrigerant to the compressor, the suction line for at least one of saidsurge drums having an accumulator interposed therein for collectingliquid refrigerant entrained with the evaporated refrigerant, a dumptrap, a booster` compressor for the dump trap, an ejector havingconnection with the accumulator for receiving liquid refrigeranttherefrom, a suction return conduit connecting the top of the dump trapwith the inlet to the booster compressor, a supply line connecting theoutlet of the booster compressor with the ejector, conduit meansconnecting the ejector with the dump trap, whereby the ejector receiveshigh pressure gaseous refrigerant from the booster compressor forpumping the liquid refrigerant received by the ejector through theconduit means for delivery to the dump trap, and other conduit means fordraining the liquid refrigerant from the dump trap and delivering thesame to the high pressure refrigerant feed line in advance of saidparallel connections.

2. in a refrigerating system, the combination with a high stagecompressor, cooling coils providing a high temperature evaporator andother separate and independent .cooling coils providing a lowtemperature evaporator, of surge drum for each of said cooling coilshaving operation to maintain its respective cooling coils in a floodedcondition for refrigerating purposes, a high pressure refrigerant feedline connecting with the compressor and providing parallel connectionsto the surge drums for delivering liquid refrigerant to the drumsrespectively, a suction line for each surge drum for returningevaporated f refrigerant to the compressor, the suction line of thesurge drum for the low temperature evaporator having an accumulatorinterposed therein for collecting liquid refrigerant entrained with theevaporated refrigerant, a dump trap, a booster compressor for the dumptrap and having a suction return conduit connecting the inlet of thebooster compressor with the trap, an ejector in connected relation withthe accumulator for receiving liquid refrigerant therefrom, a supplyline connecting the outlet of the booster compressor with the ejector,conduit means connecting the ejector with the dump trap, whereby theejector receives high pressure gaseous refrigerant from the boostercompressor for pumping the liquid refrigerant received by the ejectorthrough the conduit means for delivery to the dump trap, and otherconduit means for draining the liquid refrigerant from the dump trap anddelivering the same to the high pressure refrigerant feed line inadvance of said parallel connections.

3. A refrigerating system as dened by claim 2, additionally including anintercooler tank interposed in the suction line of the surge drum forthe high temperature evaporator, said high pressure feed line extendingthrough the tank and providing a cooling coil therein, and said feedline having a float controlled connection with the tank in advance ofthe cooling coil for delivering liquid refrigerant to the tanksufficient to maintain the cooling coil in a submerged condition. j i

4. In a refrigerating system, the combination with a high stagecompressor, cooling coils providing a high temperature evaporator andother separate and independent cooling coils providing a low temperatureevaporator, of

a surge drum for each of said cooling coils, a high pressure refrigerantfeed line from said compressor and providing parallel connections to thesurge drums, a suction line for each surge drum for returning evaporatedrefrigerant to the compressor, the suction line for at least one of saidsurge drums having an accumulator interposed therein for collectingliquid refrigerant entrained with the evaporated refrigerant, a dumptrap, a booster compressor for the dump trap and having a suction returnline connecting the inlet of the booster compressor with the trap, anejector having connection with the accumulator for receiving liquidrefrigerant therefrom, a supply line connecting the outlet of thebooster compressor with the ejector, conduit means connecting theejector with the dump trap, whereby the ejector receives high pressuregaseous refrigerant from the booster compressor for pumping the liquidrefrigerant received by the ejector through the conduit means fordelivery to the dump trap, other conduit means for draining the liquidrefrigerant from the dump trap and delivering the same to the highpressure refrigerant feed line in advance of said parallel connections,and means for introducing gaseous refrigerant from the high pressurefeed line to the dump trap for forcing the liquid refrigerant therein toow through said other conduit means.

5. In a refrigeration system, the combination with a high stagecompressor, cooling coils providing a high temperature evaporator andother separate and independent cooling coils providing a low temperatureevaporator, of a surge drum for each of said cooling coils, a highpressure refrigerant feed line connecting with the compressor' andproviding parallel connections to the surge drums for supplying liquidrefrigerant to the drums, a suction line for each surge drum forreturning evaporated refrigerant to the compressor, the suction line forthe surge drum of the low temperature evaporator having an accumulatorinterposed therein for collecting liquid refrigerant entrained with theevaporated refrigerant, a dump trap, a booster compressor for the dumptrap and having a suction return conduit connecting the inlet of thebooster compressor with the trap, an ejector in connected relation withthe accumulator for receiving liquid refrigerant therefrom, a supplyline connecting the outlet of the booster compressor with the ejector,conduit means connecting the ejector with the dump trap, whereby theejector receives high pressure gaseous refrigerant from the boostercompressor for pumping the liquid refrigerant received by the ejectorthrough the conduit means for delivery to the dump trap, other conduitmeans for draining the liquid refrigerant from the dump trap anddelivering the same to the high pressure refrigerant feed line inadvance of said parallel connections, means operable in response tochanges in the level of the liquid in the dump trap, and valve meanscontrolled by said level responsive means for closing the suction returnconduit to the trap and for introducing gaseous refrigerant from thehigh pressure feed linc to the dump trap for forcing the liquidrefrigerant therein to dow to the said fee line.

6. A refrigerating system as defined by claim 5, additionally includingan intcrcooler tank interposed in thc suction line of the surge drum forthe high temperature evaporator, said high pressure feed line extendingthrough the tank and providing a cooling coil therein, and said feedline having a oat controlled connection with the tank for deliveringliquid refrigerant to the tank suihcient to maintain the cooling coil insubmerged condition.

7. ln a refrigerating system, in combination, a high stage compressorand cooling coils providing an evaporator, a surge drum -in connectedrelation with the l1'r uid refrigerant inlet line to `the cooling coilsand with the vaporized refrigerant outlet line from the coils, a highpressure refrigerant feed line connecting the compressor with the surgedrum and supplying liquid refrigerant to the surge drum, a suctionreturn line for the vaporized refrigerant, an accumulator in the suctionreturn line for collecting liquid refrigerant so as to prevent itsdelivery to the compressor, a dump trap, a booster compressor for thedump trap, a suction return conduit connecting lthe dump trap with theinlet to the booster compressor, an ejector having connection with theaccumulator for receiving yliquid refrigerant therefrom, a supply lineconnecting the outlet of the booster com-pressor with the dump trap,said ejector being interposed in the supply line whereby high pressuregaseous refrigerant Iis delivered to the ejector for pumping the liquidrefrigerant received thereby to the dump trap, other conduit means fordraining the liquid refrigerant from the dump trap and delivering thesame to the high pressure refrigerant feed line, means operable inresponse to changes in the level of the liquid 4in the dump trap, andvalve means controlled by said level responsive means for closing thesuction return conduit to the trap and for introducing gaseousrefrigerant from the high pressure feed line to the dump trap forforcing the liquid refrigerant therein to flow to the feed line.

8. A refrigerating system as ydefined by claim 7, additionally includingdefrosting means for the cooling coils, said means comprising a valvemember in the outlet line from the cooling coils, said valve member inone position connecting said outlet line with the surge drum and inanother position connecting the outlet line with the high pressurerefrigerant feed line for introducing gaseous refrigerant to the coolingcoils, a check valve in the inlet line to the cooling coils forpreventing flow of liquid refrigerant in `a reverse direction toward thesurge drum, a conduit connecting the dump trap with the inlet line tothe cooling coils at a location beyond the check valve, and a specialcheck valve in the conduit and which opens at `an intermediate pressureto permit liquid refrigerant to flow to the dump trap 'but `which lwillclose to prevent flow of gaseous refrigerant past said special checkvalve,

9. ln a refrigerating system, in combination, a cooling coil providingan evaporator and having `a liquid refrigerant inlet line and avaporized refrigerant outlet line, a surge ldrum in connected relationwith the inlet and outlet line respectively, a high pressure refrigerantfeed iine for delivering liquid refrigerant to the surge drum, a suctionreturn line for the vaporized refrigerant, an accumulator in the suctionreturn line for collecting liquid refrigerant which may entrain with thevaporized refrigerant, a dump trap, a booster compressor for the dum-ptrap, a suction return conduit connecting the dump trap with the inletto the booster compressor, an ejector having connection with theaccumulator for receiving liquid refrigerant therefrom, a supply lineconnecting the outlet of the booster compressor with the dump `tr-ap,said ejector being interposed in the supply line whereby high pressuregaseous refrigerant from the booster compressor is `delivered to theejector for pumping the liquid refrigerant received thereby to the dumptrap, other conduit-means for draining the liquid refrigerant from thedump trap and discharging the same into the high pressure refrigerantfeed line, and defrosting means for the evaporator comprising a valvemember in the outlet line from the cooling coil, said valve member inone position connecting the outlet line with the surge drum and inanother position connecting the outlet line with the high pressurerefrigerant feed line for introducing gaseous refrigerant to the coolingcoil, a check valve in the inlet yline to the cooling coil forpreventing flow of liquid refrigerant in a reverse direction toward thesurge drum, and conduit means connecting the dump trap with the inletline to the cooling coil at a location beyond the check valve.

References Cited in the le of this patent UNITED STATES PATENTS2,589,859 Phillips Mar. 18, 1952 2,724,240 Sloan Nov. 22, l19552,778,195 Christensen Jan. 22, 1957

